Riot police firing tear gas have blocked a 1,000-strong anti-government protest in the centre of Caracas, one of 20 opposition rallies occurring across Venezuela.

Wednesday's demonstrations in the capital were the first major test of a state of emergency that President Nicolas Maduro imposed this week that gives broad powers to security forces in order to ensure public order.

The protesters were demanding authorities to stop stalling over a recall referendum called for by a petition with 1.8 million signatures. Maduro has called the referendum "not viable".

In Caracas, hundreds of officers with shields, helmets and pepper spray formed a barrier to prevent the protest, headed by opposition leader Henrique Capriles, from reaching the headquarters of the National Electoral Council (CNE), which has been parsing the petition for two weeks.

'Explosion of frustration'

A total of 14 metro stations in the heart of Caracas were closed on Wednesday for "operational reasons".

"The referendum can be held this year, and you know this. Let's avoid an explosion of public frustration," Capriles said at the demonstration.

Some police fired tear gas at the demonstrators, a few of whom threw stones and bottles. AFP news agency reporters saw at least four people arrested.

Al Jazeera's John Holman, reporting from Caracas, said the latest events will put more pressure on Maduro.

"The protesters and opposition leaders are of course calling for a referendum to remove Maduro from power. They have started the process already and are trying to push that through before the end of this year," he said.

"However, we have seen bigger numbers of people on the streets in the past. There is still not a widespread of mobilisation of Venezuelans."

Threats to security

Maduro's 60-day state of emergency was imposed on Monday to tackle what he said were threats to domestic and external security, as well as critical food and energy shortages.

He claims the adversity he is facing is manipulated by US interference working with Venezuela's "fascist" right.

Vice President Aristobulo Isturiz said the referendum was a "trap" and called on the opposition to focus on scheduled elections in December 2019.

"If you win, Maduro will give up power. Easy. What's the problem?" Isturiz said.

Protesters were demanding authorities stop stalling over a recall referendum [EPA]

Source: Al Jazeera and agencies